In many processes, different ingredients are most effective when introduced at specific points in the operation. For instance, rinse-aids or fragrances are more effective when released into the rinse cycle, rather than in the wash cycle, of a dishwashing or laundry process. One method to introduce an ingredient at a set time in the process would be to physically add it to the system when needed. Subsequent additions to a system are often not practical. Another method is to coat, encapsulate, or in some way protect the ingredient during the initial phases of an operation, then have the ingredient released at a given point due to a change in the environment triggering the removal of the protective barrier. These controlled release technologies allow all ingredients to be added to a system at one time, but released when triggered at different points in the operation. The trigger could be a change in the pH, salt concentration, or other environmental change.
WO 00/06684 describes a dishwasher detergent tablet, containing an encapsulated ingredient, where the coating has a solubility that increases with a declining concentration of a specific ion in the surrounding medium. Preferably the coating is an amine-containing polymer.
WO 00/17311 describes encapsulated detergent particles having a delayed release. The material coated is coated with a material that is insoluble in a wash solution having a pH of 10 or greater, yet soluble in a wash solution of pH 9 or less. As the wash cycle progresses, the wash pH decreases, protonating the coating material, making it more positively charged, and thus more water soluble. The increased water solubility allows the coating material to break down, releasing materials that had been encapsulated. The preferred encapsulating materials are amines, including polymeric amines.
U.S. Pat. No. 7,063,895 describes hydrophobically modified polymers of methyl methacrylate and dimethylaminopropyl methacrylate neutralized with acetic acid. The copolymer is exemplified for use as a controlled release agent.
The problem with these approaches to controlled release is that it is difficult to control the rate of dissolution of unneutralized amine materials in various pH ranges. Many amines are hydrophilic in nature even when unprotonated. This results in undesirable levels of dissolution of unneutralized amine materials even at higher pHs. Conversely, if the amine material is made more hydrophobic, it is difficult for water to penetrate films at neutral pH's. This results in a material that is not triggerable. Furthermore, these unneutralized amine materials will only be slightly protonated at both neutral and high pH in systems of low buffering capacity. This results in materials with either no solubility and trigger, or materials with an unacceptably slow, ill-defined trigger.
Surprisingly it has been found that a copolymer containing an amine functionality that is neutralized with a fixed base can form a triggerable protective layer on a material, releasing the material in a controlled manner at a given set of environmental pH and salt concentrations. The present invention has a very sharp and controllable trigger compared to the materials above which would not work in low buffering capacity systems such as detergent systems.
While not being bound by any particular theory, it is believed that after film formation, the copolymers of the present invention form a hydrophobic-hydrophilic material. The hydrophilic sections are the protonated amine monomer. The balance of the hydrophobic and hydrophilic character controls the triggering of the solubility. In alkaline water, the surface protonated amine groups on the film become deprotonated by the base present in the alkaline water. This reduces the surface solubility to the point where the polymer film cannot become swollen by the water and thus cannot dissolve. The hydrophobic comonomer aids in preventing swelling of the film. A significant amount of protonated amine groups remain in the interior of the film even in alkaline water. They are protected by the hydrophobic nature of the film and the fact that the surface protonated amine groups have become deprotonated (i.e., the film doesn't swell enough for the base in the water to penetrate the film and neutralize the interior protonated amine groups). Greater ionic strength also aids in not allowing swelling of the film. When the film is then placed in lower pH water, for example neutral water, there is less base present in the water and the film is much easier to swell due to some surface ionization at the lower pH. The water can then penetrate the film. The protonated amines in the interior of the film allow the polymer to then be dissolved in water.
Unneutralized amines with poor water solubility will not show a sharp trigger in systems of low buffering capacity. If these amines are neutralized with a volatile acid, no protonated amine will remain in the film after cure, resulting in films that are insoluble in all pH conditions. Conversely, if a water soluble amine is used, it will not show a trigger, since it will be soluble at every pH.